This invention relates to metallic composite materials and more particularly to monotectic alloys having a dispersed phase of solidification products distributed within a matrix, and to methods of producing such materials.
Numerous applications exist for composite materials having particles, rods or filaments of one metal or compound dispersed uniformly within a matrix of another. The dispersed component can be selected to provide characteristics such as superconductivity, lubricity, catalytic activity or capability for undergoing nuclear or electronic reactions, while the matrix provides required bulk properties, including structural integrity and resistance to wear and corrosion. Although the utility and advantages of such materials are readily apparent, much difficulty has been encountered in preparing them, particularly in the case of monotectic alloy systems that show a liquid miscibity gap. Methods useful for other types of alloy systems are generally ineffective for monotectic systems because of gravity-induced segregation, which results in non-uniform distribution of the dispersed component.
Various prior workers have reported preparation of monotectic alloys having an aligned microstructure by means of directional solidification, with the dispersed phase taking the form of filaments or rods, or in some cases irregular drops. Rod-like structures have been obtained by solidification of monotectics of the Bi-Se system, Knight et al, Transactions of the Metallurgical Society--AIME, Vol. 245 (1969) at 351; the Cu-Cu.sub.2 S system, Marich et al, Metallurgical Transactions, Vol. 2 (1971) at 2681; and the Sb-Se system (Lemkey, U.S. Pat. No. 3,434,827), but the structures obtained are of irregular spacing or sizing. Prior techniques for controlling the distribution of rods or spheres of a minor constituent of an alloy which separates in the liquid phase owing to liquid phase immiscibility and density differences were thought to be limited to the relatively few systems in which a second liquid phase (L.sub.II) is trapped by an advancing planar interface during directional solidification. Provision of a method of controlling distribution which does not require an inherent capability for entrapment of the second liquid phase would make available many monotectic alloy systems that have not been amenable to fabrication into useful articles.
It is therefore an object of this invention to provide monotectic alloys having the minor component thereof uniformly dispersed in the form of particles or rods in a matrix of the major component.
Another object is to provide a process for preparing monotectic alloys wherein the distribution, shape and size of the dispersed component are controlled.
Still another object is to provide a directional solidification process for preparation of monotectic alloys in which control of distribution of particles of the dispersed component is not dependent upon inherent entrapment of the second liquid phase at an advancing planar interface.